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THESIS 



THE PHYSICAL OCEANOGRAPHY 
OF THE 

NORTHERN BAFFIN BAY-NARES STRAIT 


REGION 


by 




Victor G. Addison, Jr. 




December 1987 




Thesis Advisor 


R.H. Bourke 



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Naval Ocean Systems Center 
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This thesis was prepared in conjunction with research sponsored by the 
Arctic Submarine Laboratory, Naval Ocean Systems Center, San Diego, California 
under Work Order N66001 - 86-WR-00131 . Reproduction of all or part of this 
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THE PHYSICAL 0CEAN0CRAPHY OF THE NORTHERN BAFFIN BAY-NARES STRAIT REGION 



\ PERSONAL AUTHOR(S) 








Addision, Victor G., 


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Master’s Thesis 


CROM TO 


1987 December 


110 



> SUPPLEMENTARY NOTATION 

Prepared in conjunction with R.H. Bourke and R.G. Paquette 



COSATI CODES 



FIELD 


GROUP 


SUB-GROUP 















16 SUBJECT TERMS (Continue on reverse i> necessity end identity py brock number) 



Baffin Bay 
Nares Strait 



SIR JOHN FRANKLIN 
North Water 



) ABSTRACT (Continue on reverse it necessity tnd identity o y block numoer) 

A dense network of conductivity-temperature-depth (CTD) measurements was conducted from 
.affin Bay northward to 82 t ’09’N at the entrance to the Lincoln Sea, in most comprehensive 
hysical oceanographic survey ever performed in the northern Baffin Bav-Nares Strait (NBB-NS) 
egion. These data indicate Nares Strait Atlantic Intermediate Water (NSATW) and Arctic 
asin Polar Water (ABPW) to be derived from Arctic Basin waters via the Canadian Archipelago, 
'hereas the West Greenland (WGC) is the source of the comparatively dilute West Greenland 
iurrent Atlantic Intermediate Water (WGCAIW) and West Greenland Current Polar Water (WGCPW) 
tactions. Baffin Bay Surface Water (BBSW) is found seasonally throughout northern Baffin 
iay. Recurvature of component branches of the WGC, which attains a maximum baroclinic 
ransport of 0.7 Sv, occurs primarily in Melville Bay (0.2 Sv) , south of the Carey Islands 
0.1 Sv) and ultimately in Smith Sound (0.2 Sv). The Baffin Current originates as an 
ce-edge jet in Smith Sound and is augmented by net outflow from Smith, Jones, and Lancaster 
ounds at rates of 0.3 Sv, 0.3 Sv and 1.1 Sv, respectively. Circulation in Smith, Jones and 



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Block 18 (continued) 

Geostrophic Estuarine Circulation 
Lancaster Sound 
Jones Sound 



Smith Sound 
Kane Basin 
Melville Bay 



Block 19 (continued) 

Lancaster Sounds can be described in terms of the Geostrophic Estuarine 
Circulation Model (GEC) . The North Water is caused by the combined influences 
of near-surface layer enthalpy and mechanical ice removal. 



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Approved for public release; distribution is unlimited. 



The Physical Oceanography of the 
Northern Baffin Bay-Nares Strait Region 



by 

Victor G. Addison, Jr. 

Lieutenant, United States Navy 
B.S., State University of New York, Stony Brook, 1979 



Submitted in partial fulfillment of the 
requirements for the degree of 

MASTER OF SCIENCE IN METEOROLOGY AND OCEANOGRAPHY 



from the 



NAVAL POSTGRADUATE SCHOOL 
December 1987 



abstract 



^ ) 



A dense network of conductivity-temperature-depth (CTD) measurements 

was conducted from Baffin Bay northward to 82’09'N at the entrance to 
the Lincoln Sea, in the most comprehensive physical oceanographic survey 
ever performed in the northern Baffin Bay-Nares Strait (NBB-NS ) region. 
These data indicate Nares Strait Atlantic Intermediate Water (NSAIW) and 
Arctic Basin Polar Water (ABPW) to be derived from Arctic Basin waters 
via the Canadian Archipelago, whereas the West Greenland Current (WGC) 
is the source of the comparatively dilute West Greenland Current 
Atlantic Intermediate Water (WGCAIW) and West Greenland Current Polar 
Water (WGCPW) fractions. Baffin Bay Surface Water (BBSW) is found 
seasonally throughout northern Baffin Bay. Recurvature of component 
branches of the WGC, which attains a maximum baroclimc transpoit of 
0.7 Sv, occurs primarily in Melville Bay (0.2 Sv) , south of the Carey 
Islands (0.1 Sv) and ultimately in Smith Sound (0.2 Sv) . The Baffin 
Current originates as an ice-edge jet in Smith Sound and is augmented by 
net outflow from Smith, Jones, and Lancaster Sounds at rates of 0 . 3 Sv, 
0.3 Sv and 1.1 Sv, respectively. Circulation in Smith, Jones and 
Lancaster Sounds can be described in terms of the Geostrophic Estuarine 
Circulation Model (GEC) . The North Water is caused by the combined 
influences of near-surface layer enthalpy and mechanical ice removal. 



4 



T> 



TABLE OF CONTENTS 



I . INTRODUCTION 12 

A. PURPOSE 12 

B. BACKGROUND 13 

1. Bathymetry 15 

2. General Circulation 16 

3. Water Masses 19 

4. The North Water 20 

II. METHODS AND MEASUREMENTS 23 

A. CRUISE SUMMARY 23 

B. INSTRUMENTATION 23 

C. DATA REDUCTION AND ANALYSIS 25 

III. THERMOHALINE STRUCTURE 28 

A. INTRODUCTION 28 

B. BAFFIN BAY SURFACE WATER 28 

C. POLAR WATER 34 

D. ATLANTIC INTERMEDIATE WATER 53 

IV. CIRCULATION AND TRANSPORT 58 

A. INTRODUCTION 58 

B. DYNAMIC TOPOGRAPHY 58 

C. THE WEST GREENLAND CURRENT 61 

D. CIRCULATION IN NARES STRAIT 65 

E. THE BAFFIN CURRENT 70 

F. CIRCULATION IN THE SOUNDS 71 

1 . Introduction 71 



5 



2. Smith Sound 71 

3 . Jones Sound 73 

4. Lancaster Sound 75 

5. Geostrophic Estuarine Circulation 75 

G. BAROCLINIC TRANSPORTS 82 

V. THE NORTH WATER PROCESS 88 

VI. DISCUSSION 92 

VII . CONCLUSIONS 94 

APPENDIX: COMPUTATIONS ASSOCIATED WITH THE GEC MODEL 96 

LIST OF REFERENCES 98 

INITIAL DISTRIBUTION LIST 100 



6 



LIST OF TABLES 



I. NEAR-SURFACE AND INTERMEDIATE- DEPTH WATERS OF THE NORTHERN 



BAFFIN BAY-NARES STRAIT REGION 29 

II. GEOSTROPHIC ESTUARINE CIRCULATION MODEL CALCULATIONS 79 



7 



LIST OF FIGURES 



1.1 A chart of the northern Baffin Bay-Nares Strait region 14 

1.2 The West Greenland Current and the Baffin Current (from 

Muench, 1971, p. 2) 17 

1.3 The approximate monthly mean extent of the North Water 

(from Dunbar, 1970, P- 279) 21 

2.1 The locations of CTD stations conducted during the September 

1986 cruise of CCGS SIR JOHN FRANKLIN 24 

2.2 The locations of transects used in the analysis 26 

3.1 A composite temperature profile illustrating the shallow 

thermocline characteristic o t BBSW 31 

3.2 The horizontal distribution of maximum temperatures in 

the BBSW layer 32 

3.3 A T/S transect northeastward across Melville Bay 33 

3.4 A meridional T/S transect from Baffin Bay northward to 

Kane Basin 35 

3.5 A composite salinity profile illustrating the dilution of 

WGCPW relative to ABPW 37 

3.6 A composite densitv profile illustrating the dilution of 

WGCPW reLative to ABPW 38 

3.7 A composite T/S curve illustrating knee salinities 

characteristic of WGCPW and ABPW 39 

3.8 A composite T/S curve illustrating the absence of a sharp 

knee in stations north of Smith Sound 41 

3. g The horizontal distribution of ABPW and WGCPW in the NBB-NS 

region 42 

3.10 A composite temperature profile illustrating the interleaving 
of ABPW and WGCPW in Smith Sound. Jones Sound and 

Melville Ba v 44 

3.11 A T/S transect northward across Melville Bav 45 

3.12 A T/S transect across Kane Basin 46 

3.13 A T/S transect across the southern entrance to Kane Basin.... 48 



8 



3.14 A T/S transect across the mouth of Jones Sound 49 

3.15 A T/S transect across the mouth of Lancaster Sound 50 

3.16 A composite density profile illustrating the magnitude of 

glacial mel twater- induced stair-stepped layering in Kane 
Basin 51 

3.17 A T/S transect in Robeson Channel 52 

3.18 The horizontal distribution of NSAIW and WGCAIW in the 

NBB-NS region 54 

3.19 A meridional T/S transect from Kane Basin northward 

through Kennedy and Robeson Channels 56 

3.20 A T/S transect Jones Sound eastward to Thule 57 

4.1 Surface circulation in the NBB-NS region 59 

4.2 The surface dynamic topography referenced to 200 

decibars, in dynamic centimeters 60 

4.3 A baroclinic velocity cross section through Melville Bay 63 

4.4 A baroclinic velocity cross section from Jones Sound 

eastward to Thule. 64 

4.5 A meridional baroclinic velocity cross section from Baffin 

Bay northward to Kane Basin 66 

4.6 A baroclinic velocity cross section through a southern 

part of Kennedy Channel 67 

4.7 A baroclinic velocity cross section through Che southern 

portion of the Kane Basin Gyre 69 

4.8 A baroclinic velocity cross section through Smith Sound 72 

4.9 A baroclinic velocity cross section through Jones Sound 74 

4.10 A baroclinic velocity cross section through Lancaster Sound.. 76 

4.11 A schematic cross section of coastal upper layer flow 

(from Leblond, 1980, p. 191) 77 

4.12 Surface dynamic height anomalies in Lancaster Sound 
(in dynamic cm) relative to 300 dbar level (from 

Fisse'l et al., 1982, p. 187) 80 

4.13 Dvnamic topography of the surface relative to 500 dbars in 

Jones Sound for various years (from Mueneh. 19 7 L. p. 92) 8 3 



9 



4.14 Major baroclinic transports in the NBB-NS region .....85 

5.1 Enthalpy of the near-surface (upper 75 m) layer in the 

NBB-NS region (referenced to 1.8°C) 90 



10 



ACKNOWLEDGEMENTS 



Funding for the work described in this thesis was provided by the 
Arctic Submarine Laboratory, Naval Ocean Systems Center, San Diego, 
California under Work Order N- 66001 - 86 -WR00131 . 

I wish to thank Dr. R.H. Bourke for initially providing me with the 
opportunity to participate in this study, and, thereafter, for his 
invaluable assistance and encouragement. Dr. R.G. Paquette is also 
gratefully acknowledged for his advice and assistance and, in 
particular, for this continued support during periods of severe personal 
hardship . 

The success of the cruise can be attributed to the enthusiasm and 
dedication of the Captain and crew of the CCGS SIR JOHN FRANKLIN. I 
also wish to thank A.M. Weigel, K.O. McCoy and Dr. P. Jones for their 
innumerable personal contributions to this effort. Miss J.E. Bennett is 
also gratefully acknowledged for her indispensable assistance in the 
preparation of this manuscript. 

Finally. I wish to thank my lovely wife, Karen, for being there when 
I needed her. 



11 



I. imQDVCTIQE 



A. PURPOSE 

During September 1986, the CCGS SIR JOHN FRANKLIN conducted an 
oceanographic measurement program from Baffin Bay northward into Nares 
Strait, to the southern reaches of the Lincoln Sea. This expedition 
marked the first comprehensive use of continuous profiling conduc tivi ty- 
temperature -depth (CTD) measurements throughout the region, and the 
northernmost transit (82°09'N) of a surface ship through Nares Strait 
since the 1971 voyage of the CCGS LOUIS S. ST. LAURENT. Sponsorship of 
this endeavor was provided by the Arctic Submarine Laboratory, with 
diplomatic concurrence from the governments of Canada and Denmark. 

The principal objective of the cruise was to examine the 
distribution of physical oceanographic variables from Baffin Bay 
northward, in order to determine the circulation and water mass 
characteristics of the region. The successful transit of the region by 
the SIR JOHN FRANKLIN provides a data set from which it is possible, 
essentially for the first time, to thoroughly define the baroclinic 
circulation and water mass structure of the northern Baffin Bay-Nares 
Strait region. 

Specific objectives of the analysis will be to: (1) define the 

trajectory, transport and extent of the West Greenland and Baffin 
Currents; (2) describe the charac teristics and extent of the water 
masses found throughout the region: (3) characterize the role of 

topographic steering and bathymetric boundaries on baroclinic 



12 



circulation and water mass penetration; (4) present a model which 
explains the observed circulation in Smith, Jones, and Lancaster 
Sounds; and (5) present a hypothesis for the formation and maintenance 
of the North Water, a large polynya located in Northern Baffin Bay. 

B . BACKGROUND 

The northern Baffin Bay-Nares Strait (hereinafter referred to as 
NBB-NS) region is historically significant for a number of seemingly 
unrelated reasons (Figure 1.1). Lancaster Sound, noted as the 
traditional Atlantic entrance to the Northwest Passage and as a net 
source of Arctic Ocean water inflow to the region, remains relatively 
ice free during winter. Indeed, northern Baffin Bay as a whole was 
thought to remain conspicuously unencumbered by ice during the winter 
due to the presence of the North Water. The Humboldt Glacier, the 
largest glacier in the northern hemisphere, is located on the eastern 
side of Nares Strait and is the source for many of the icebergs which 
are observed throughout the NBB-NS region. Once calved from the 
glacier, many of these icebergs travel southward past Cape York, in 
defiance of the northward flowing West Greenland Current. The most 
comprehensive oceanographic analysis of the northern Baffin Bay region 
is provided by Muench (1971). Muench's work serves as a summary of all 
significant oceanographic research conducted prior to 1971, and has been 
referenced in all subsequent analyses of the NBB-NS region. 

Prior to 1972, all baroclinic oceanographic analyses in the NBB-NS 
region were derived from bottle sampling techniques. The CCGS LOUIS S. 
ST. LAURENT obtained discrete measurements of temperature and salinity 
in Nares Strait during August 1971, reaching a latitude of 82°56'N 



13 




Figure 1.1 A chart of the northern Baffin Bay-Nares 

Strait region. Ice concentrations greater than 
7/10 (during the FRANKLIN 86 cruise) are 
represented as shaded areas. 



14 



(Sadler, 1976). During 1972, scientific personnel aboard the LOUIS S. 
ST. LAURENT obtained the first winter oceanographic data from Davis 
Strait utilizing an in situ salinity/temperature/depth unit (STD) 

(Muench and Sadler, 1973). Transports through Nares Strait have been 
investigated by Sadler (1976), providing the most accurate current meter 
derived estimates of Lincoln Sea inflow to the region. In 1978 and 
1979, the Eastern Arctic Marine Environment Studies (EAMES) program 
utilized current meters and CTD stations to investigate the southward 
flowing Baffin Current (Fissel et al . , 1982). Research concerning the 
processes leading to the formation of the North Water has most recently 
been conducted by Steffen and Ohmura (1983). 

1. Bathymetry 

The bottom topography of the NBB-NS region is complex and, as 
such, has the potential to exert significant control over physical 
oceanographic processes. The influence of glaciers on all aspects of 
the morphology of this region is quite obvious. 

Northern Baffin Bay is fed by Lancaster and Jones Sounds to the 
west, and Smith Sound to the north. Shoaling to depths of less than 
200 m occurs at some point in both Lancaster and Jones Sounds, 
effectively restricting deeper Arctic Ocean inflow. A sill which ranges 
in depth from 160 m to 200 m is present at the southern end of Kennedy 
Channel, providing similar constraints on Lincoln Sea inflow to the 
region. Similarly, shoaling to a depth of 230 m occurs at the Smith 
Sound entrance to Kane Basin. 

The deep, relatively flat central portion of northern Baffin 
Bay is punctuated in its eastern portion l»v i shallow *700 in) bank 



15 



located in Melville Bay. A deep (500 m to 900 m) channel passes 
offshore from Cape York, terminating northward in Smith Sound. To the 
west, the mouths of Jones and Lancaster Sounds reach depths of 700 m, 
but the bottom northeast of Devon Island shoals to less than 200 m 
approaching Smith Sound. 

2. General Circulation 

The baroclinic circulation pattern in the NBB-NS region is 
dominated by the northward flowing West Greenland Current (WGC) and the 
southward flowing Baffin Current (Figure 1.2). Augmenting the transport 
of the Baffin Current are net outflows from Jones and Lancaster Sounds, 
coupled with southward flow through Nares Strait. The net baroclinic 
transport through northern Baffin Bay has been computed to be 
approximately 2.0 Sv (10 6 m 3 s _1 ) southward (Muench, 1971). Muench 
postulated that this transport is driven by a higher surface elevation 
in the Arctic Ocean relative to that in Baffin Bay, presumed to be a 
consequence of differing water structures in their respective upper 
250 m layers. 

Bottom topography, predominantly northerly winds, and meltwater 
admixture are thought to play variable roles in the maintenance of a 
cyclonic circulation pattern in northern Baffin Bay. The WGC, a 
significantly barotropic current, may be enhanced baroclinically by 
near-shore low salinity wedges of meltwater. Alternately, the Baffin 
Current exhibits the increased baroclinic intensity characteristically 
found in western boundary currents. The westward turning of the WGC off 
Cape York, and the southward turning of Lancaster Sound outflow, are 
both influenced by topographic steering < Muench. 1 L, 71). 



16 




Figure 1.2 



The West Greenland Current and the Baffin 
Current (from Muench, 1971, p. 2). 



17 



Circulation features in the NBB-NS region may be subject to 
seasonal variations. Lemon and Fissel (1982) noted a general winter 
weakening of near- surface baroclinic currents by a factor of two or 
more. The WGC , which transports northward only 10% of the baroclinic 
volume transported southward by the Baffin Current, is not always 
present during late summer (Muench, 1971). 

The directional components of some features of the surface and 
baroclinic flow fields are temporally variable. Muench stated that 
reversals of baroclinic flow have been observed in Smith and Jones 
Sounds, while reversals of surface flow have occurred in Smith Sound. 
Lancaster Sound, however, consistently provides net inflow to Baffin Bay 
on the order of twice that of Smith or Jones Sounds (Muench, 1971). 
Anticyclonic eddies (sometimes referred to as counter currents) have 
been reported near Bylot Island (Fissel et al . , 1982), while cyclonic 
eddies have been observed off Cape York (Muench, 1971). 

Current speeds in the NBB-NS region, although variable, are 
consistently greatest in magnitude near eastern Lancaster Sound. Fissel 
et al . (1982), using current meters, found near-surface velocities of 
0.75 m/sec in the portion of the Baffin Current located east of 
Lancaster Sound. Directly measured current speeds in Nares Strait are 
extremely variable in magnitude, with maximum near-surface values 
ranging from 0.1 to 0.60 m/sec (Sadler, 1976). Maximum baroclinic 
velocities in the WGC are on the order of 0.1 m/sec (Muench, 1971). 

The nature and vertical extent of the flow regimes in the 
NBB-NS region are spatially complex. Although the vertical extent of 
volume flow in the WGC probably reaches a depth ot 500 m. most 



18 



baroclinic flow is limited to the upper 100 m (Muench, 1971). The 
Baffin Current nominally extends to a depth of 500 m, with flow reaching 
the bottom (700 m to 840 m deep) in the region of its intrusion into 
Lancaster Sound (Fissel et al . , 1982). Significant baroclinic flow in 
this current is associated with the upper few hundred meters (Muench, 
1971). The flow in Nares Strait has a substantial baroclinic component 
which reaches to depths of 300 m (Sadler, 1976). 

3. Water Masses 

Adopting the usual convention for Arctic regions, Muench (1971) 
divided the waters of northern Baffin Bay into three layers: a cold 

(<0°C) upper Arctic Water layer; a warmer (>0°C) intermediate -depth 
Atlantic Water layer; and a cold (<0°C) Deep Water Layer. The Arctic 
Water, confined to the upper 200 m to 300 m, has an upper limit in 
salinity of approximately 34.0. The Atlantic Water extends from the 
bottom of the Arctic Water layer to depths of 700 m in Lancaster Sound 
and 1300 m in northern Baffin Bay, exhibiting salinities of 34.2 to 
34.5. Baffin Bay Deep Water extends from the bottom of the Atlantic 
Layer to the seabed, and is characteristically isohaline at 34.48. 

The density of water masses in the NBB-NS region, as in other 
Arctic regions, is primarily determined by salinity. Surface and near- 
surface layers, therefore, are usually characterized by strong 
haloclines and associated pycnoclines. The delineation of a surface 
(upper 75 m) layer of Arctic Water, which is modified by boundary layer 
processes, has been suggested by Fissel et al. (1982). Since diverse 
processes such as solar heating, meltwater admixture, and wind mixing 



19 



play roles in the formation of this layer, its temperature and salinity 
characteristics vary seasonally. 

The thermohaline characteristics of the water masses of the 
region can generally be traced to their sources, while their horizontal 
extent is often determined by bathymetric effects. Arctic Water is 
water of Arctic Ocean origin which either entered Baffin Bay via Davis 
Strait and was modified by cooling and admixture of runoff within 
northern Baffin Bay, or was modified by cooling and freshening within 
the Arctic Ocean prior to entering Baffin Bay from the north. Mixing of 
inflowing Arctic Ocean Water and resident Baffin Bay Arctic Water of the 
same density occurs in southern Smith Sound, Jones Sound, and Lancaster 
Sound. Shallow sills present in Lancaster Sound, Jones Sound and 
Kennedy Channel prevent southward flow of Arctic Ocean Atlantic Water 
into Baffin Bay. Atlantic Water in northern Baffin Bay, therefore, 
originates from the Atlantic Ocean via Davis Strait (Muench, 1971). 

4. The North Water 

Extensive interest has been focused on a persistent polynya , 
termed the North Water, which is located in northern Baffin Bay 
(Figure 1.3). Dunbar (1970) concluded that the polynya is defined by a 
stable northern boundary at the Smith Sound entrance to Kane Basin, and 
a consistent western ice edge which forms along Ellesmere Island. The 
locations of the eastern and southern boundaries are seasonally 
dependent. Significant penetration of the North Water occurs westward 
into Lancaster Sound in June. The phenomenon is less well defined 
during the summer season after ice break up commences. Contrary to 
earlier reports, the North Water region is not completely open during 



20 




Figure 1.3 The approximate mean monthly extent of the North 

Water in: March (...), April ( ), May 

( — ), June ( ); (from Dunbar. 1970, p. 

279). 



21 



winter, and is characterized by extensive areas of new ice formation 
(Dunbar, 1973). Steffen and Ohmura (1985) used thermal infrared 
measurements from an airplane in winter to determine that the North 
Water was mostly covered with new and young ice, and probably devoid of 
first year ice until March. The ice surface, they surmised, was 
approximately 20°C warmer than that of the surrounding fast ice. 

The North Water essentially remains an unexplained phenomenon. 
Muench (1971) computed a heat budget for the region and concluded that 
insufficient heat is present in the Atlantic Water layer in northern 
Baffin Bay to prevent ice formation. He similarly concluded that there 
was not enough heat present in the surface Arctic Water layer either, 
and postulated mechanical ice removal by northerly winds and currents as 
the effects responsible for the formation of the North Water. Dunbar 
(1973) reinforced this hypothesis by noting that the age and thickness 
of ice increases from the Smith Sound ice arch southward. Steffen and 
Ohmura (1985), however, computed more accurate heat budgets for the 
region and concluded that oceanic heat of unknown origin is responsible 
for the formation and maintenance of this polynya . 



22 



II. METHODS AND MEASUREMENTS 



A. CRUISE SUMMARY 

Between 7 and 27 September 1986, the CCGS SIR JOHN FRANKLIN 
conducted the most extensive physical oceanographic survey ever 
performed in the NBB-NS region. The SIR JOHN FRANKLIN covered over 
4000 km in the course of conducting 145 CTD stations (Figure 2.1; refer 
to Figure 2.2 for station number identification). Numerous transects 
were performed while transiting from Lancaster Sound northward to 
Robeson Channel, and subsequently southward to Melville Bay. Ice 
reconnaissance was provided by the SIR JOHN FRANKLIN's embarked 
helicopter, which was instrumental in enabling the ship to penetrate 
Robeson Channel to 82°09'N; the furthest northward of any ice breaker 
since 1972. 

B. INSTRUMENTATION 

The instruments used were the Applied Micro Systems Limited 
Conductivi ty -Temperature - Depth recorder, model STD- 12. This instrument 
has a stated accuracy of 0.02 mS/cm in electrical conductivity, 0.01°C 
in temperature and no stated accuracy in depth. The resolutions were 
stated to be 0.003 mS/cm, 0.001°C, and 0.05 dbar , respectively. 

Three instruments, numbered 422, 433 and 467, respectively, were 
utilized during the cruise. CTD //433 is the property of the Naval 
Postgraduate School (NPS), and was calibrated both before and after the 
cruise with resultant errors of 0.003°C in temperature and 0.007 mS/cm 
in conductivity. Calibrations for the other two instruments were not 
initially available, and were obtained empirically in the form of first 



23 




gure 2.1 



The locations of CTD stations conducted during the 
September 1986 cruise of CCGS SIR JOHN FRANKLIN. 



degree polynomials by intercomparison with CTD #433 during simultaneous 
lowerings. It is concluded that the absolute error in the variables 
issmaller than 0.02°C, 0.02 mS/cm, and 2.0 dbars . The root mean square 
error in salinity, therefore, is approximately 0.03. 

The data were recorded internally in coded binary form, and were 
downloaded into a Compaq computer for conversion into engineering units 
and storage on 5.25 in. floppy diskettes. Each CTD was programmed to 
sample the data stream every 0.8 dbar of pressure change. Significantly 
finer resolution in pressure was not convenient because of computer 
memory limitations and downloading time constraints. 

The primary navigation aid was the ship's Magnavox MX 1107 Satellite 
Navigation System. An average of two fixes per hour provided a mean 
navigational accuracy of 0.5 km. 

C. DATA REDUCTION AND ANALYSIS 

Upon completion of the cruise, the data were transferred to mass 
storage cartridges for further processing with the NPS IBM 3033 
computer. Editing of spurious and mis - sequenced data points, the cause 
of which is discussed by Tunnicliffe (1985), was subsequently performed. 
Removal of dynamic response errors in temperature and salinity was 
accomplished as prescribed by Bourke et al . (1986). The edited profile 
data were then sub-sampled every 5 m for use in the production of 
baroclinic velocity profiles and related volume transport estimates. 

Transects used in the data analysis for the construction of vertical 
sections are depicted in Figure 2.2. Temperature -salinity (T/S) 
transects are oriented as noted, with temperature values (°C) 
represented as solid lines and salinity values (Practical Salinity 



25 




Figure 2.2 The locations of transects used in the analysis. 

The dotted line denotes stations used for 
construction of meridional cross sections. 



26 



Scale) represented as dashed lines. Baroclinic velocity cross sections 
are oriented with velocities (cm /sec) "into" and "out of" the page 
represented as solid (positive values) and dashed (negative values), 
respectively . 

Surface dynamic heights and baroclinic velocity profiles were 
derived from the geostrophic approximation, assuming a level of no 
motion of 200 dbars . The technique of Helland -Hansen (1934) was deemed 
inappropriate for use in the NBB-NS region because of the inherently 
shallow and irregular bathymetry, thereby precluding the selection of a 
deeper reference level for regional application. Although a 200 dbar 
reference level is suitable for estimating direction in near-surface 
baroclinic currents, magnitudes were found to be underestimated by as 
much as 25% when compared to those derived with a level of no motion of 
400 dbars . 

Baroclinic volume transports were calculated using variable 
reference levels, determined by the maximum common sample depth in a 
station pair. As the sample depths were occasionally limited by 
mechanical rather than bathymetric considerations, the associated 
transports may be subject to underestimation accordingly. The 
transports were calculated by vertical trapezoidal integration of 
baroclinic velocities over 5 m intervals. 



27 



III. THERMOHALINE STRUCTURE 



A. INTRODUCTION 

In order to more accurately characterize the near-surface and 
intermediate depth waters of the NBB-NS region, a delineation of five 
discrete water masses by vertical distribution of temperature and 
salinity is required (Table I). Baffin Bay Surface Water (BBSW) is 
derived locally and found seasonally in northern Baffin Bay at depths of 
up to 75 m. It is present in both the Baffin Current and the WGC . 

In general, the water masses which uniquely comprise the WGC are found 
to be less saline than their counterparts which enter the NBB-NS region 
through the Canadian Archipelago. Although the salinity difference 
between the Polar Water fractions is small, it is useful as a 
classification tool. Mixing of Arctic Basin Polar Water (ABPW) and West 
Greenland Current Polar Water (WGCPW) should be expected to occur along 
isopycnal surfaces in regions where their domains overlap. Although the 
salinity distributions of Nares Strait Atlantic Intermediate Water 
(NSAIW) and West Greenland Current Atlantic Intermediate Water (WGCAIW) 
do not intersect, it is bathymetry which prevents mixing of these two 
source fractions. 

B. BAFFIN BAY SURFACE WATER 

Baffin Bay Surface Water (BBSW) is locally derived from the combined 
effects of meltwater admixture and solar heating. The large, ubiquitous 
glaciers in the NBB-NS region serve as a continuous source of meltwater 
during periods of insolation. Admixture of glacial runoff with Baffin 
Bay Polar Water (BBPW) creates a significant halooline and resultant 
pycnocline in the upper 50 m to 75 m of the water column. Concurrently, 



28 



TABLE I NEAR-SURFACE AND INTERMEDIATE DEPTH WATERS OF THE NORTHERN BAFFIN BAY-NARES STRAIT REGION 









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29 



•West Greenland Current T: > 0°C ‘Generally warmer than NSAIW 

Atlantic Intermediate S: 33.8 - 34.5 

Water (WGCAIW) D: 250 m - 800 m 



the effects of solar heating are essentially confined to this surface 
layer due to its inherent buoyancy. The admittedly arbitrary 
delineation of BBSW by the 0°C isotherm serves to distinguish it from 
BBPW, rather than imply that the effects of insolation are restricted to 
a discrete temperature range. BBSW is best identified, however, by the 
presence of a strong, shallow thermocline (Figure 3.1). A seasonal 
reversal of the processes which create BBSW, ultimately results in its 
elimination. 

The distribution of BBSW is a regional phenomenon. The horizontal 
distribution of maximum temperatures in the BBSW layer shows distinct 
gradients in the meridional and offshore directions (Figure 3.2). This 
result implies that BBSW is formed primarily by coastal processes, and 
is subsequently advected throughout most of northern Baffin Bay. The 
complete absence of BBSW north of Smith Sound is due to the widespread 
occurrence of pack ice, which serves to raise the albedo of the region 
and reduce insolation. 

The considerable concentration of BBSW located in the shelf waters 
of Melville Bay contributes significantly to the baroclinici ty of the 
WGC . A qualitative examination of a T/S transect through Melville Bay 
not only indicates that a major portion of the baroclinicity occurs in 
the upper 100 m, but that the isohalines (isopycnals) related to the 
presence of BBSW assume a negative slope in the core of the WGC between 
Stations 122 and 123 (Figure 3.3). The seasonal presence of BBSW, 
therefore, would be expected to enhance the baroclinic transport of the 
WGC. 



30 



o 

rsi 




i 

o 



o 

o 

o 



o 

o 

oo 



o 

o 

o 

n 



o 



□ 

□ 



o 

o 

LD 



(W) Hld30 



O 

• 

_ r\) 
i 



o 

o 

o 

CD 



31 



Figure 3.1 A composite temperature profile illustrating the 

shallow thermocline characteristic of BBSW. 
Refer to Figure 2.2 for station location. 




Figure 3.2 The horizontal distribution of maximum 
temperatures in the BBSW layer. 



32 




33 



DISTANCE (Km) 

Figure 3.3 A T/S transect northeastward across Melville Bay. 

Temperature contours are indicated by solid lines 
and salinity contours by dashed lines. 



The presence of BBSW at an ice edge can be considered to represent 
an equilibrium state. The northernmost extent of BBSW is precisely 
correlated with the location of the pack ice edge. A meridional T/S 
transect from Baffin Bay northward to Kane Basin graphically illustrates 
this interaction between relatively warm surface water and an ice edge 
(Figure 3.4). A filament of BBSW dives subsurface between Stations 44 
and 47 beneath water of lower density at the ice edge. An equilibrium 
state can exist if sufficient thermal advection is present to prevent 
ice growth. Mitigation of thermal advection or atmospheric cooling will 
cause the ice edge to advance or retreat, respectively. 

C. POLAR WATER 

Polar Water in the NBB-NS region is derived from two distinct 
sources. Direct inflow from the Arctic Ocean through the Canadian 
Archipelago is generically classified as Arctic Basin Polar Water 
(ABPW), whereas northward flow via the WGC through Davis Strait is 
termed West Greenland Current Polar Water (WGCPW) . Subtle contrasts in 
the thermohaline signatures of these two water masses are indicative of 
their different origins, and serve as qualitative tracers of their 
respective flow fields. 

Although both forms of Polar Water have origins in the Arctic Ocean, 
the flow of WGCPW follows a circuitous route around the southern tip of 
Greenland before entering the NBB-NS region. The cumulative influence 
of shelf and surf ace -dr iven processes on the thermohaline structure of 
WGCPW is, therefore, of greater magnitude than the effect of similar 
processes on ABPW. The primary modification which occurs is due to 
meltwater admixture, resulting in a net dilution of the water column. 



34 



irr fpr.r 

STA NO 22 28 32 41 44 147 




<<•>) HldX 



35 



Figure 3.U A meridional T/S transect from Baffin Bay northward 

to Kane Basin. 



Viewed simpl is tically , WGCPW can be considered a diluted form of ABPW . 
The comparative decrease in salinity and, hence, density of WGCPW below 
the surface layer is most apparent in vertical property profiles 
(Figures 3.5 and 3.6). The maximum salinity of WGCPW is approximately 
34.2, while ABPW reaches 34.8. 

The presence of Polar Water with an underlying warm layer produces 
a characteristic inflection, or knee, when temperature is plotted 
against salinity. This knee can be viewed as a boundary between the 
bottom of the arctic halocline, formed as a consequence of convective 
overturn in winter, and a deeper thermocline, which marks the transition 
to an underlying warm layer. The salinity and depth at which this knee 
occurs are functions of the inherent thermohaline characteristics of the 
particular Polar Water mass. The combination of relatively dilute WGCPW 
and underlying Atlantic Intermediate Water results in a knee with a 
salinity of 33.4 to 33.5, at depths ranging typically from 50 m to 120 
m. As ABPW enters the NBB-NS region through Lancaster Sound, for 
instance, it is subject to interleaving and mixing along isopycnal 
surfaces. This comparatively undiluted inflow is characteristically 
more dense than the resident Polar Water of northern Baffin Bay, and 
consequently sinks. The resultant combination of comparatively saline 
ABPW and underlying Atlantic Intermediate Water produces a knee with 
salinities between 33.5 and 33.7, at depths of up to 250 m. A composite 
T/S curve illustrates the contrasting knee salinity ranges of WGCPW and 
ABPW (Figure 3.7). 

A reduction in significant insolation in the near -surface laver. or 
the absence an underlying warm laver. will result in a weaker thermal 



36 



o 




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o 



o 

o 

CO 



o 

o 

to 



o 

o 



o 

o 

in 



CD 

o 

CD 



(W) HId30 



37 



Figure 3.5 A composite salinity profile illustrating the 

dilution of WGCPW (Stations 122 and 140) relative to 
ABPW (Stations 6 and 87). 



o 




o 



o 

o 



o 


o 


o 


o 


o 


o 


o 


o 


o 


o 


oo 


CO 




in 


CD 



(N) Hld3Q 



38 



Figure 3.6 A composite density profile illustrating the 

dilution of WGCPW (Stations 122 and 140) relative to 
ABPW (Stations 6 and 87). 




o 




>-• 

h-* 



CH 



oo 



PO 



(3) 3UrUUy3dU3I 



39 



Figure 3.7 A composite T/S curve illustrating knee salinities 

characteristic of WO’CFW (Stations 138 and 142), an 
ABPW (Stations 4 and 6). 



gradient and a bend, rather than a sharply defined knee, in the curve. 
This condition is apparent north of Smith Sound due to the widespread 
occurrence of pack ice, with an associated increase in albedo 
(Figure 3.8). 

The thermohaline characteristics of the two Polar Water masses can 
be used to roughly estimate the horizontal extent of their flow 
regimes. A plan view of Polar Water distributions indicates that inflow 
of WGCPW represents the minority fraction of Polar Water in the NBB-NS 
region (Figure 3.9). WGCPW is prevalent along the West Coast of 
Greenland northward to Cape York, where a bifurcation in flow creates 
one filament which extends to Smith Sound and another which projects 
westward into Jones Sound. Northward passage of WGCPW into Kane Basin 
was not observed. 

ABPW is present from the Lincoln Sea to the southern end of Kane 
Basin, and throughout the central and western portions of Baffin Bay. 

The presence of ABPW at stations north of 77°N not only suggests that 
Smith Sound is a mixing site for the two Polar Water masses, but is 
indicative of southward passage of ABPW from Nares Strait into northern 
Baffin Bay. Inflow of ABPW is restricted to the southernmost portion of 
Jones Sound, implying significant mixing there as well. Inflow of ABPW 
to the region is greatest in Lancaster Sound, as indicated by the 
consistently high knee salinities encountered there. A filament of 
ABPW can be seen in the southwestern corner of Melville Bay at Stations 
132 and 133, which marks the location of a frontal boundary between an 
extreme northeastern branch of the Baffin Current, possibly derived from 
Lancaster Sound outflow, and a southward flowing branch of the WGC . The 



40 



o 




(f) o oj n n 
13 LO CD CD CD 
0 OGOO 

♦ — i 

f— I 

^ 1 « I I 

CO o < + X 



I 

o 

CM 



■ LO 

ro 



m 

ro 

o 

■ TT* 

ro 



■ ro 
ro 



■ ro 
ro 



LO 



o 

o 



i 

o 

CM 



>H 

h- 



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ro 



. CO 



• CM 

ro 



LO 

ro 

o 

ro 

LO 

h- o 
ro 



o 
. ro 



(0) 3ynibb3dU3I 



41 



Figure 3.8 A composite T/S curve illustrating the absence of 

sharp knee in stations north of Smith Sound. 




Figure 3.9 



The horizontal distribution of ABPW and WGCPW in the 
NBB-NS region. 



42 



extensive interleaving which would be expected in regions such as these, 
where ABPW and WGCPW coexist, is evident in composite temperature 
profiles (Figure 3.10). 

The presence of subsurface temperature extremes in the Polar Water 
layer is associated with the contrasting effects of convective overturn 
in winter and insolation in summer. Convective overturn during ice 
formation creates a cold, isohaline layer which can project to a depth 
of greater than 50 m locally. Lateral infusion of brine produced during 
the freezing of shelf waters can increase the vertical extent of this 
isohaline layer to over 100 m. Subsequent surface heating and meltwater 
mixture produces significant enthalpy increases in the shallow 
pycnocline layer only, isolating an underlying cold lens at depths 
typically between 50 m and 150 m. 

South of Smith Sound cold lenses are sharply defined by strong 
temperature gradients. This is typically the case in Melville Bay, 
where cold, isohaline water is sandwiched between an overlying layer of 
BBSW and an underlying layer of Atlantic Intermediate Water 
(Figure 3.11). 

The absence of cold lenses north of Smith Sound is indicative of 
the inherently persistent ice cover. The associated high albedo 
results in steadily decreasing temperatures towards the surface and, 
consequently, no subsurface cold lenses are apparent north of 
Station 72, located at approximately 79.2°N (Figure 3.12). 

Southward decreases in ice concentration result in the formation of 
diffuse cold lenses in northern Smith Sound. A T/S transect taken at 
the southern entrance to Kane Basin reveals the remnants of a subsurface 



43 



o 

rsj 




cun HIcGO 






44 



Figure 3.10 A composite temperature profile illustrating the 

interleaving of ABPW and WGCPW in Smith Sound 
(Station 42), Jones Sound (Station 16), and Melville 
Bay (Station 133) . 





45 



Figure 3.11 A T/S transect northward across Melville Bay. 



ON Vl$ MN 




O 



O 

O 

co 



O 

o 



(*) 



o 

o 

U5 



Hld30 



o 

o 

CD 



o 

o 

o 



46 



Figure 3.12 A T/S transect across Kane Basin. Note the absence 
of a subsurface cold lens . 



cold lens on the western side, and alternating warm and cold layers to 
the east (Figure 3.13). 

Pronounced warm lenses are located on the southern side of 
Lancaster Sound, and along both boundaries of Jones Sound. Conditions 
in Jones Sound, with ambient air temperatures averaging -4°C and the 
presence of new ice observed along both shores, indicate that the local 
occurrence of subsurface lenses of BBSW is due to the initiation of 
convective overturn (Figure 3.14). The warm lens in southern Lancaster 
Sound is a sharply defined feature located at a depth of approximately 
10(> m (Figure 3.15). The depth of this warm lens indicates that it is 
probably an outflow jet of ABPW which dives subsurface upon 
encountering a cooler, but comparatively less saline layer of resident 
Polar Water. This effect further illustrates the point that ABPW is 
more saline than the residual Polar Water mixture of northern Baffin 
Bay, and is subject to mixing along isopycnals at deeper depths. 

The major source of meltwater in the NBB-NS region is the Humboldt 
Glacier, located on the eastern side of Kane Basin. All stations in 
Kane Basin south of approximately 79°56'N (Station 84) have low surface 
salinities, typically approaching 31.0, and exhibit significant stair- 
stepped layering in vertical density structure (Figure 3.16). This not 
only illustrates the magnitude of glacial influence in the region, but 
suggests that extensive recirculation of near-surface waters may occur 
in Kane Basin. A significant local source of meltwater is apparent in 
the northwest corner of Robeson Channel, where surface salinities were 
generally below 30.0, the lowest encountered in the NBB-NS region 
(Figure 3.17). 



47 



DEPTH (m) 



NW STA NO 55 56 57 58 59 SE 




Figure 3.13 A T/S transect across the southern entrance to Kane 
Basin. Note the remnant of a cold lens at Station 
55, and alternating warm and cold layers to the 
east . 



48 



S STA. NO. 13 14 15 16 N 




Figure 3.14 A T/S transect across the mouth of Jones Sound. 



49 



DEPTH (m) 



S STA. NO. I 2 3 4 5 6 7 8 N 




Figure 3.15 A T/S transect across the mouth of Lancaster 
Sound . 



50 



o 




o 

o 



o 

o 

r\] 



o 

o 

ro 



o 

o 



o 

o 

in 



o 

o 

CD 



t W) Hld30 



51 



Figure 3.16 A composite density profile illustrating the magnitude of 
glacial meltwater-induced stair-stepped layering in Kane 
Bn sin. 



S STA. NO. 105 103 99 N 




Figure 3.17 A T/S transect in Robeson Channel. 



52 



D. ATLANTIC INTERMEDIATE WATER 



The two Atlantic Intermediate Water fractions found in the NBB-NS 
region exhibit inherently different salinity characteristics and 
exclusive horizontal distributions. Nares Strait Atlantic Intermediate 
Water (NSAIW) is derived from the Atlantic Layer of the Arctic Basin 
and flows southward from the Lincoln Sea into Nares Strait. West 
Greenland Current Atlantic Intermediate Water (WGCAIW) flows northward 
through eastern Davis Strait, advected by the WGC into northern Baffin 
Bay . 

WGCAIW is warmer but less saline than NSAIW. Following the same 
line of reasoning which requires subdivision of the Polar Water 
fractions, WGCAIW is subject to more significant dilution effects by 
shelf and surf ace -dr iven processes compared to direct inflow from the 
Arctic Basin. Since CTD cast depths were not deep enough to reach the 
bottom of the WGCAIW layer, the upper limit in salinity presented in 
Table I for this water mass should be considered an estimate. The 
maximum salinity encountered in WGCAIW was 34. 44, at a depth of 562 m 
(Station 124), whereas a maximum salinity of 35.24 was recorded for 
NSAIW at a depth of 481 in (station 97). The comparatively lower 
temperatures in NSAIW are a reflection of the general north- south 
temperature gradient in the region. The highest Atlantic Layer 
temperature recorded in NSAIW was 0.20°C at a depth of 715 m 
(Station 95), in contrast with a maximum temperature of 1.81°C, recorded 
at a depth of 445 m (Station 133) for WGCAIW. 

The horizontal distributions of NSAIW and WGCAIW in the NBB-NS 
region are primarily determined by topographic ini iuences (Figure 3.18). 



53 



z 




Figure 3.18 



The horizontal distribution of NSAIW and WGCAIW 
in the NBB-NS region. 



54 



Southward passage of NSAIW into Kane Basin is prevented by shoaling of 
the sea floor in southern Kennedy Channel (Figure 3.19). Although the 
major portion of WGCAIW flow is turned cyclonically to the southwest by 
the coastlines of Melville Bay and Cape York, northward transport of the 
remainder is abruptly terminated by a shallow bank (200 m) located in 
the vicinity of the Carey Islands. Northward flow of WGCAIW could 
continue to follow a deep narrow channel around this bank (Figure 3.20). 
but was not observed to do so. Once turned to the southwest, the flow 
of WGCAIW throughout northern Baffin Bay is not restricted by 
bathymetry. It should be noted that even with the hypothetical 
occurrence of westward flow from Cape York, penetration into Jones Sound 
by WGCAIW would be impossible because of shallow banks located east of 
the mouth. The flow into Lancaster Sound, however, is not similarly 
restricted. It is apparent that southeastern Lancaster Sound is a site 
of significant interleaving of dissimilar water masses, as the 
associated T/S cross section reveals the presence of BBSW, ABPW, and 
WGCAIW in profile (refer to Figure 3.15). It is presumed that WGCAIW is 
present at stations 7, 8, 9, 10 and 11, although the shallow CTD casts 
at these stations precludes absolute confirmation. 



55 




T3 

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aQ 



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O 

4-1 



u 

0 / 

w 



00 

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c 

T3 



CL 

< 



OC 



56 



through Kennedy and Robeson Channels. The meridional 




Cl 

Oy 



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4-J 0) 



T 5 

i-l 

ft >. 

3 -O 

^ -c 

r: 

0 / C 

— i 
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57 



isotherm) is confined to a narrow channel. 



IV. CIRCULATION AND TRANSPORT 



A. INTRODUCTION 

Macroscale circulation in the NBB-NS region is dominated by the 
northward flowing WGC and the southward flowing Baffin Current. 

Although net southward flow in the region is maintained primarily by 
baroclinic forcing (Muench, 1971), bathymetry exerts considerable 
influence on the formation of mesoscale circulation patterns. An 
examination of the surface circulation of the region, as deduced from 
baroclinic velocity and dynamic height calculations, reveals the natuie 
of this influence (Figure 4.1). Reference to this surface circulation 
diagram is implied in the ensuing discussions. 

B. DYNAMIC TOPOGRAPHY 

An examination of the surface dynamic topography of the NBB-NS 
region referenced to 200 dbars indicates a general westward increase in 
dynamic heights (Figure 4.2). This trend is associated with the 
influence of the Coriolis force on the net southward flow. 

The shoreward gradient of the dynamic height contours, in northern 
Baffin Bay lends a cyclonic appearance to the circulation pattern. 
Meltwater runoff may be responsible for the increase in dynamic heights 
along the coastline of Melville Bay. The complex circulation patterns 
associated with the WGC are inferred from the reversal of gradients and 
bending of contours in the vicinity of Cape York. Northwestward flow 
around Cape York is diverted cyclonicallv to the south in the vicinity 
of the Carey Islands, an event associated with the limitation of 
northward flow of WGCAIW in the region :onthw<ud ( lowing branch of 

the WGC is clearly evident in Melville Bay. The flow reversal occurs on 



58 




Figure 4.1 Surface circulation in the NBB-NS region as deduced from 
baroclinic velocity and dynamic height calculations. 



59 




Figure 4.2 The surface dynamic topography referenced to 200 

decibars, in dynamic centimeters. 



60 



the perimeter of a shallow bank, suggesting a possible topographic 
influence. Westward intrusions of surface flow are apparent at the 
northern sides of the entrances to both Lancaster and Jones Sounds. 
Although net flow is eastward in both cases, the closer spacing of 
contours in Lancaster Sound is associated with much greater baroclinic 
velocities. A significant portion of the ABPW outflow from Jones Sound 
into northern Baffin Bay is turned anticyclonical ly around the southeast 
shore of Devon Island, augmenting the westward intrusion of flow into 
Lancaster Sound. 

The sharp bending of contours in Smith Sound marks the boundary 
between two intersecting circulation regimes. A northward flowing 
branch of the WGC turns cyclonical ly , coincident with the formation of 
an ice-edge jet at the southern limit of the ice pack. The 0.36 dynamic 
meter contour is representative of the impingement of the relatively 
warm surface current on the ice pack, with a resultant density gradient 
normal to the ice edge. The deflection of southward flow from Nares 
Strait at the front is also apparent, but determination of associated 
circulation patterns within Kane Basin is not possible at this 
resolution. The meandering 0.28 dynamic meter contour in Kane Basin, 
however, is suggestive of the potential for gyre formation in this 
region . 

C. THE WEST GREENLAND CURRENT 

Circulation of the WGC in northern Baffin Bay appears to be 
governed by conservation of potential vorticitv. As a typical eastern 
boundary current, the WGC mav be assumed t o hrv a substantial 
barotropic component of flow. Conservation oi potential vorticity 



61 



requires barotropic flow to follow lines of constant f/H, where f is the 
Coriolis parameter, and H is the water depth. Since mesoscale 
variations in the Coriolis parameter can be considered negligible, flow 
will tend to parallel isobaths. 

Justification of the preceeding assumptions in the case of the WCC 
is provided by a number of observations. Although the direction of mean 
flow in the WGC is closely correlated with the 500 m isobath, 
recurvature to the west and south is noted at three primary locations. 

In Melville Bay the flow is observed to recurve southeastward around a 
shallow bank. A cross section of baroclinic velocities in this area not 
only indicates significant deep flow around the periphery of the bank, 
but confirms the filamental nature of the return current (Figure 4.3). 
The two distinct flow regimes on the southwest side of the bank are, as 
stated in Chapter 3, of different origins. Flow between Stations 128 
and 129 is a recurved branch of the WGC which, assuming conservation of 
relative vorticity, probably forms a cyclonic gyre around the perimeter 
of the bank. Southwest of an apparent frontal boundary, however, a 
second axis of flow exists which has been shown to principally contain 
ABPW. 

Shoaling of the bottom in the vicinity of the Carey Islands causes 
complete recurvature of WGCAIW. The baroclinic velocity cross section 
from Jones Sound westward to Thule reveals that the core of the WGC is 
found east of Station 22 (Figure 4.4). Since water of Atlantic Laver 
origin has been confirmed between Stations 21 and 24. recurved flow of 
WGCAIW must pass between Stations 21 and 22. Calculation of baroclinic 
velocities between Stations 21 and 2 2. "i f h a of no motion assumed 



62 



STA. NO 131 130 



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63 



from the geos trophic approximation, assuming a level of no 
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64 



at 375 m, indicates that southward flow for this station pair is limited 
to the upper 55 in of the water column. Northward flow between 
Stations 22 and 23, calculated with a level of no motion at 400 in, 
decreased from 0.12 m/s at the surface to less than 0.03 m/s at a depth 
of 115 m. The implication of this result is that most baroclinici ty in 
the WGC is confined to the surface and near-surface layers. Barotropic 
currents are presumed to dominate below this level, hence, the 
postulated influence of topographic steering on the WGC. 

The remaining branch of the WGC is recurved at the northern extent 
of the 500 m isobath in Smith Sound. A meridional velocity cross 
section through the region further substantiates the classification of 
the baroclinic component of this flow as an ice edge jet (Figure 4.5). 
Baroclinic velocities between Stations 41 and 44, calculated with a 
level of no motion at 400 m, decreased from 0.44 m/s at the surface to 
approximately 0.04 m/s at 200 m. Below 200 m, predominantly barotropic 
flow is topographically steered to the west and south by rapid shoaling 
of the bottom. 

D. CIRCULATION IN NARES STRAIT 

The macroscale circulation regime in Nares Strait generates net 
southward flow of ABPW into Smith Sound. Mesoscale circulation patterns 
in the region, however, can not be characterized so succinctly. 

Inflow from the Lincoln Sea proceeds southward through Robeson and 
Kennedy Channels. A baroclinic velocity cross section through a 
southern part of Kennedy Channel indicates the relatively uniform nature 
of this flow (Figure 4.6). Recalling that southward Mow of NSAfW is 
terminated by rapid shoaling just north of this transect (refer to 



65 




66 



Figure 6.5 A meridional baroclinlc velocity cross section from Baffin 
Bny northward to Kane Basin. Fositive isotarhs indicate 
flow to the west . 



W, STA. NO. 88 87 86 




DISTANCE ( KM ) 



E 



Figure 4.6 A baroclinic velocity cross section through a 

southern part of Kennedy Channel. 



67 



Figure 3.19), it is probable that the relatively high current speeds in 
this area are associated with constriction of flow. Furthermore, 
shoaling is more extreme on the eastern side of the channel resulting in 
correspondingly higher speeds. In contrast, the high baroclinic current 
speed in Robeson Channel is probably due to the influence of the 
previously described local concentration of meltwater. 

Circulation in Kane Basin is characterized by southward flow in two 
peripheral branches, surrounding a central cyclonic gyre. Circulation 
along the eastern side of Kane Basin is topographically steered 
southward along the inherently shallow seabed. Augmented by runoff from 
the Humboldt Glacier, this eastern branch continues southwes tward and 
merges with recurved WGC water in Smith Sound. The flow of the western 
branch is also bathyme trically influenced. A portion of this branch 
turns cyclonically along the 200 m isobath forming a gyre, while the 
remainder continues southward, merging with both the western branch and 
the recurved WGC. The southern portion of the gyre is quite apparent in 
a baroclinic velocity cross section through Kane Basin (Figure 4.7). 

In contrast to its effect on the WGC, topographic steering does not 
appear to play as strong a role in Kane Basin. This implies that 
circulation within Kane Basin has a significant baroclinic component of 
flow. This presumption is most apparent between Stations 74 and 76, at 
the northern edge of the gyre. Baroclinic velocities between these 
stations reverse from southward at the surface, to northward below 65 in 
depth. This vertical shear in velocities is indicative of baroclinic 
instability, which might serve as a potential energy source for either 
the Kane Basin Gyre or smaller, undn t er f ^<1 *ddi«~s. 



68 



NW STA 




69 



Figure 4.7 A baroclinic velocity cross section through the 

southern portion of the Kane Basin Gyre. 



E. THE BAFFIN CURRENT 



The Baffin Current originates in Smith Sound, where southwest ward 
flow from Nares Strait merges with recurved WGC water. During its 
progression southward, the Baffin Current is augmented by outflows 
from Jones and Lancaster Sounds, and by WGC water which has recurved 
sou h of Smith Sound. 

As a typical western boundary current, the Baffin Current can be 
considered highly baroclinic. A baroclinic velocity profile between 
Stations 28 and 29, assuming a level of no motion at 400 m, indicates 
surface flow of 0.19 m/sec steadily decreasing to 0.5 m/sec at 200 m. 
Unlike the WGC, significant barocl inici ty in the Baffin Current is not 
coni ined to the upper 100 m. 

Interaction between the Coriolis force and bathymetry provides the 
primary steering influence for the Baffin Current. Throughout the 
course of the current, the tendency for westward turning by the Coriolis 
forte is offset by the presence of a lateral boundary. At the northern 
entrance to Jones and Lancaster Sounds, however, the removal of this 
restriction permits the observed westward intrusion of flow. It should 
be emphasized, however, that the barotropic component of flow associated 
with the Baffin current is not negligible. An examination of the 
baroclinic velocity cross section from Jones Sound eastward to Thule 
provides three clear cases of topographic steering (in conjunction with 
Figure 4.4, refer to Figure 4.1). Although a branch of the Baffin 
Current turns westward into Jones Sound, the main core of the current 
proceeds southward between Stations 18 and 1°. restricted bv 



70 



bathymetry. Also apparent are two cyclonic gyres; one around Coburg 
Island, and the other in the vicinity of a 150 m bank. 

Eastward outflow from the south side of Jones Sound subsequently 
merges with the main core of the Baffin Current along the coast of Devon 
Island. In contrast to the narrow filament entering Jones Sound, the 
major branch of the Baffin Current forms the westward intrusion of flow 
into Lancaster Sound. 

F. CIRCULATION IN THE SOUNDS 

1 . Introduction 

Smith, Jones and Lancaster Sounds are all considered regions of 
net volume inflow to northern Baffin Bay. An examination of the 
circulation characteristics associated with each sound will provide a 
basis for their comparison. 

2 . Smi th Sou nd 

Within Smith Sound exists a frontal boundary separating 
southward flowing ABPW and recurved WGC water. Circulation in this 
region, therefore, is determined primarily by baroclinic influences. A 
baroclinic velocity cross section through Smith Sound reveals a weak 
core between Stations 41 and 42 which is actually the remaining branch 
of the northward flowing WGC (Figure 4.8). Complete recurvature of this 
branch occurs just north of Station 41. Southward flow between Stations 
42 and 43 is a filament of ABPW from the east branch of circulation in 
Kane Basin. The interaction between recurved BBSW and southwes twa rd 
flowing ABPW is marked by the presence oi a distinct ice edge. Indeed, 
the impingement of warm BBSW on the ire « dg* rrmtos a meltwater 
gradient which loccally elevates the dynamic heights, providing a strong 



71 



ON VIS 




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72 



Figure 6.8 A barocltnic velocity cross section through Smith Sound. 



baroclinic influence on flow direction. The resultant formation of an 



ice edge jet between Stations 40 and 41 marks the origin of the Baffin 
Current. Augmentation of the Baffin Current by ABPW occurs beneath the 
shallow pycnocline, which is associated with relatively warm, buoyant 
BBSW from the WGC (refer to Figure 3.4). 

Significant bathymetric influence in Smith Sound is limited to 
positioning of the frontal boundary between the two circulation regimes. 
Although topographic steering along the 500 m isobath clearly influences 
re< urvature of the WGC, baroclinic effects are responsible for the 
formation of the Baffin Current. Smith Sound, therefore, is the site 
where a significantly barotropic circulation regime is transformed into 
a predominantly baroclinic one. 

3 . Jones Sound 

The combined influence of bathymetry and the Coriolis force on 
the circulation structure of Jones Sound is most apparent in a cross 
section of baroclinic velocities (Figure 4.9). A filament of the Baffin 
Current is deflected westward by the Coriolis force around the 
southeast corner of Ellesmere Island and into Jones Sound north of 
Station 15. Eastward outflow of ABPW is restricted to the south of 
Station 15, continuing along the east coast of Devon Island. The 
presence of a cyclonic gyre around Coburg Island (refer to Figure 4.1) 
links the flow paths accordingly. 

While eastward outflow from Jones Sound tends to follow the 
500 m isobath, the westward intrusion is driven by the Coriolis force 
over a 200 m bank, against prevailing westerly winds. The baroclinic 



73 




Figure 4.9 A baroclinic velocity cross section through Jones Sound. 



74 



velocity cross section illustrates the relatively shallow nature of this 
westward intrusion of flow. 



4. Lancaster Sound 

Circulation in Lancaster Sound is characterized by a westward 
intrusion of flow between Stations 6 and 8, and an eastward return 
current of greater magnitude between Stations 1 and 6 (Figure 4.10). 

The increase in velocities towards the sides of the sound indicates the 
effect of the Coriolis force on the inflow and outflow branches. 
Baroclinic velocities in the outflow branch are the highest in the 
entire NBB-NS region, reaching a maximum of 0.78 m/sec at the surface 
between Stations 2 and 3 (assuming a level of no motion at 340 m) . 

5 . GeQ g tT.QB I nc Egtyigr in e Ci ircu iet j Qn 

Although their thermohaline and bathymetric features are 
inherently different, the general characteristics of circulation in 
Smith, Jones and Lancaster Sounds are remarkably similar. In each case, 
geos trophically balanced inflow is entrained, in estuarine fashion, by 
geos trophically balanced outflow. A quasi -vert ical frontal feature 
initially separates the two current regimes, the slope of which is 
determined by their respective velocity structures (refer, for example, 
to Figure 4.10). The dynamic aspects of the ensuing model, hereinafter 
referred to as Geostrophic Estuarine Circulation (GEC), are derived 
from the work of Leblond (1980). Variations in the observed character 
of the circulation in each sound can be explained in terms of how 
closely local conditions approximate GEC. 

In proposing a two layer ’’Coastal Current Model" to explain the 
observed circulation in some channels of the Canadian Archipelago. 



75 



ON VIS 



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76 



DISTANCE ( KM ) 



Leblond showed that two geostrophically balanced, upper-layer flows 
would coexist without interference in a channel whose width is 
sufficiently large compared to the local internal Rossby radius of 
deformation. Restriction of flow to the upper layer creates a sloped 
interfacial surface, resulting in a characteristically wedge-shaped 
velocity structure (Figure 4.11). 



I 




Figure 4.11 A schematic cross section of coastal upper 
layer flow (out of the page) of speed u, 
driven by a sea surface slope tj( y) The 
lower layer of density p 2 is at rest because 
the interface h(y) slopes in a direction 
opposite to that of the free surface. Y c 
is the distance from the coast at which the 
thickness of the upper layer vanishes (from 
Leblond, 1980, p. 191). 

Additionally, Leblond found that purely geostrophic flow can turn 
corners without separating from a coast if the radius of curvature of 
the coast is large enough that the Rossbv number remains well below 
unity. As a conservative estimate of the width of a coastal geostrophic 
current, V Q is defined as Y Q - R/F ; where R is the internal Rossby 
radius of deformation and F is the internal Froude number. If the width 
of a channel is shown to exceed 2 ( Y 0 ) , two geos trophical 1 v balanced 
upper-layer flows can theoretically exist without interference. 



77 



The results of applying L blond's equations to Smith, Jones and 
Lancaster Sounds are listed in Table II, with the requisite 
calculations presented in the Appendix. Since the computed Rossby 
number (R 0 ) at the mouths of all three sounds is less than 0.1, 
nonlinear effects may be locally neglected. It should be noted that 
values of Y Q are only calculated for the outflow regimes which, in each 
sound, were the widest of the two currents. 

Conditions in Lancaster Sound, with a minimum channel width (L) 
of 80 km, and a geostrophic cui rent width (Y Q ) of 20.35 km, most closely 
approximate GEC . Referring to the baroclinic velocity cross section 
through Lancaster Sound (Figure 4.10), it clear that although the 
calculated value of Y Q is considered an underestimation of the width of 
the outflow current, interference between the two circulation regimes 
appears negligible. The obvious wedge-shaped current structure implies 
that flow is primarily restricted to the upper 150 m. The broadening of 
the outflow wedge beyond the calculated value of V Q , however, indicates 
that this restriction is not complete. Indeed, the likelihood of 
significant flow occurring below 250 m depth is confirmed by the 
presence of WGCAIW in western Lancaster Sound. 

Entrainment of inflow results in cyclonic cross - channel flow. 
The connection of inflow and outflow currents in Lancaster Sound by 
cross-channel flow was most recently investigated by Fissel et al. 
(1982), who found the westward extent of the inflow intrusion strongly 
marked by dynamic height anomalies (Figure 4.12). This result 
illustrates that, in GEC, cyclonic cross - channel flow associated with 
entrainment of inflow is a geos trophica l 1 v balanced process. The 



78 



TABLE II GEOSTROPHIC ESTUARINE CIRCULATION MODEL CALCULATIONS 



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80 



Figure 4.12 Surface dynamic height anomalies in eastern Lancaster 

Sound (in dynamic cm) relative to the 300 dbar level for 
four periods of CTD observations in 1979: (A) July 18-1 

(B) July 29 - August 3; (C) September 2-4; and (D) 
September 14-23 (from Fissel et al . , 1982, p. 187). 



convergence of inflow and outflow regimes creates a local elevation in 
the sea surface, generating geos trophic flow normal to the resultant 
pressure gradient. With sufficient eastward outflow and the presence of 
lateral boundaries, characteristic cyclonic flow will result. Since 
convergence implies downwelling, a reduction in vertical density 
gradients may occur along this frontal feature, thereby enhancing the 
tendency for mixing. 

In Lancaster Sound the eastward outflow branch of the 
circulation illustrates the increase in volume and velocity typically 
associated with estuarine entrainment. In GEC, however, the entrainment 
is geostrophically , not turbulently, driven. 

The application of GEC to Smith Sound is influenced by both 
geometric constraints and significant horizontal density gradients. 
Referring to Table II, it is apparent that L is approximately equal to 
2 (Y 0 ) . Since this is considered a minimum requirement, the potential 
for interference between the inflow and outflow regimes may be 
significant. This interference may manifest itself in the form of 
baroclinic instability and associated eddy generation. 

Within Smith Sound the inflow and outflow regimes are not 
appreciably influenced by coastal boundaries. The absence of a 
characteristically wedge-shaped velocity structure in this region is 
probably a consequence of this fact. Geostrophy does influence the 
direction of the inflow and outflow branches, however, resulting in 
cyclonic cross -channel flow. As stated previously, recurvature of the 
remaining branch of the WGC occurs as the result of an extreme 
horizontal density gradient at the ice-ed;;e Lront. Entrainment of WGC 



81 



inflow in Smith Sound, while not directly attributed to convergence, is 
nonetheless geos trophically balanced. 

The limitations in applying G EC to Jones Sound are 
considerable. Since L < 2(Y Q ), Jones Sound is wide enough to 
accommodate only one geos trophically-balanced current Referring to the 
33.0 isohaline in Figure 3.14, the formation of densi y and, hence, 
baroclinic velocity wedges is evident at the sides of the channel; 
however, a complete blurring of the structure occurs between Stations 14 
and 15. Since these current branches can not coexist in Jones Sound, it 
may be possible for complete intrusion of the westward inflow branch to 
occur at times, resulting in reversal of the net eastward flow in Jones 
Sound. Historical evidence of this occurrence has been cited by Muench 
(1971) (Figure 4.13). In 1962, for example, the flow is entirely 
westward, while in 1963 both inflow and outflow are present 
simultaneously but with the outflow dominant. 

The macroscale circulation pattern in the NBB-NS region can 
also be envisioned as conforming to the GEC model. Viewed 
simplistically , the inflowing waters of the WGC are geos trophical ly 
entrained at various latitudes, subsequently resulting in the augmented 
outflow which characterizes the Baffin Current. The predictably 
cyclonic circulation pattern associated with GEC is identifiable as a 
major macroscale feature in the region. 

G. BAROCLINIC TRANSPORTS 

Baroclinic transports derived from various arbitrary reference 
levels should be used, onlv with great reluctance, to infer continuity 
of volume. This is especially true in eastern boundary current regions, 



S2 




0 / 



oD 

u. 



83 



Dynamic topography of the surface relative to 300 dbars in 
Jones Sound for various years; (from Muench, 1971, p. 92). 



like the WGC , where the baroclinici ty is known to be weak. The main 
purpose of this section, therefore, will be to qualitatively compare the 
baroclinic components of flow for major currents in the NBB-NS region. 
Unless otherwise specified, subsequent references to transports are 
summarized in plan view and assumed to be baroclinic in nature 
(Figure 4.14). 

The WGC achieves maximum transport in Melville Bay, prior to its 
previously described pattern of recurvature in northern Baffin Bay and 
Smith Sound. Transport of the WGC consequently decreases from a 
maximum of 0.7 Sv in Melville Bay, to 0.4 Sv in the vicinity of the 
Carey Islands, and 0.2 Sv in Smith Sound. The major portion of 
baroclinic transport is concentrated at the extreme inshore stations in 
Melville Bay, further substantiating the assumption that glacial runoff 
is primarily responsible for this component of WGC flow. 

The Baffin Current is partially derived from the net southward flow 
of Nares Strait. Southward transport increases from 0.2 Sv in Robeson 
Channel to 0.7 Sv at the mouth of Kennedy Channel. This increase may be 
attributed to admixture of meltwater runoff, in particular from 
Petermann's Glacier, located on the eastern shore of Robeson Channel. 
Southward transport through Kane Basin is primarily associated with the 
western circulation branch (0.3 Sv) , while southward transport in the 
eastern circulation branch is limited (0.1 Sv) . The swirl transport 
within the Kane Basin Gyre is approximately 0.4 Sv, indicative of its 
effect in recirculating meltwater from the Humboldt Glacier throughout 
the basin. The cyclonic ice-edge jet in Smith Sound, with associated 
transport of 0.5 Sv, can be considered as GEG outflow from Nares Strait 



84 




Figure 4.14 



Major baroclinic transports in the NBB-NS 
region. 



85 



which is augmented by entrainment of the remainder of the WGC (0.2 Sv) . 
Net southward outflow from Kane Basin through Smith Sound, therefore, is 
inferred to be approximately 0.3 Sv. 

The Baffin Current, which becomes an identifiable feature in Smith 
Sound, continues southward along the coast of Ellesmere Island where 
transport is measured as 1.0 Sv . The formation of a topographically- 
induced cyclonic gyre is coincident with branching of the Baffin 
Currentnor theas t of Coburg Island. A westward flowing filament (0.1 Sv) 
enters Jones Sound, where it is entrained and augmented by eastward 
outflow (0.4 Sv) , resulting in net eastward transport of 0.3 Sv . A 
southwes tward flowing branch ( ).2 Sv) probably follows the 500 m 
isobath, subsequently merging with the main core of the Baffin Current. 
The relatively large transport (0.7 Sv) indicated southwest of Melville 
Bay is actually an algebraic summation of transports obtained between 
Stations 127 and 132 (refer to Figure 4.3). Southeastward transport of 
Baffin Current water (0.4 Sv) , probably derived from a branch of 
Lancaster Sound outflow which is topographically steered eastward along 
the 1000 m isobath (Muench, 1971), is apparent southwest of Station 130. 
Flow of WGC water, which has recurved either around the shallow bank in 
Melville Bay (0.2 Sv) or south of the Carey Islands (0.1 Sv) , is 
indicated between Stations 127 and 129. 

The main core of the Baffin Current, augmented by eastward outflow 
from Jones Sound, follows the southwest coast of Devon Island westward 
into Lancaster Sound (0.6 Sv) . GEC entrainment and subsequent 
augmentation of outflow yields gross eastward outflow of 1.7 Sv . Net 



86 



transport in Lancaster Sound, therefore, is inferred to be 1 . 1 Sv 



eastward . 



87 



V. THE NORTH WATER PROCESS 



The North Water Process is characterized by complex interaction 
between thermohaline and dynamic effects. The net result of this 
process is the demarcation of an 80,000 km 2 arctic region which is 
conspicuously devoid of first year ice from the onset of winter until 
March (Steffen and Ohmura . 1985). Following a brief examination of some 
relevant factors, a qualitative description of the process will be 
presented . 

In southern Baffin Bay freezing is generally accompanied by the 
formation of an isothermal isohaline near-surface layer approximately 75 
m to 100 m in depth (Garrison et al . , 1976). Sea-ice production in the 
NBB-NS region is similarly associated with the formation of such deep 
mixed layers (Muench, 1971). In the weakly stratified waters of Nares 
Strait, convective processes are sufficient to form this homogenous 
layer. The region south of Smith Sound, however, is characterized by 
the ubiquitous occurrence of BBSW. The resultant presence of such a 
strong pycnocline would ordinarily limit the depth of convective mixing 
associated with surface freezing to much less than 75 m. A combination 
of turbulent and convective processes must be required, therefore, to 
overcome the inherent stability of this buoyant layer and produce the 
observed deep mixed layers. 

Given a particular set of climatic conditions, the enthalpy present 
in the near-surface layer determines the length of time required to 
initiate surface freezing. Assuming heat flux onlv through the surface 
and neglecting thermal advection, it is possible to evaluate this tiim* 
delay as a function of heat budget parameter-. St el ten and Ohmura 



88 



(1985) computed monthly and annual heat budgets for the North Water 
region and concluded, assuming a reference temperature of -1.8°C, that 
the amount of oceanic heat flux required to prevent ice formation is 
337.4 MJM'2 i n October and 445.1 MJM'^ in November. The enthalpy 
contained in the 75-m deep, near-surface layer was calculated, 
referenced to -1.8°C, for all FRANKLIN 86 stations (Figure 5.1). For 22 
stations located southward of Smith Sound, between 76° N and 78° N, the 
enthalpy in September averaged 475 MJ . Applying the aforementioned heat 
budget at the onset of winter (October), implies that surface freezing 
would be delayed by approximately five weeks in this region. In 
contrast, the average enthalpy contained in the ice -covered, near- 
surface layer north of 78°N (Nares Strait) was 120 M J . 

The presence of mechanical ice removal effects such as divergent 
currents and winds will cause the rate of sea-ice production to greatly 
exceed the rate of sea ice accumulation for a given area. This 
phenomena is graphically illustrated in the vicinity of the Kane Basil 
Gyre where cyclonic and, hence, divergent circulation results in an area 
of reduced ice concentration. Ice concentrations within the gyre were 
typically 3/10 or less, compared with surrounding concentrations of 
greater than 5/10. The cyclonic macroscale circulation pattern 
characteristic of northern Baffin Bay can be expected to provide a 
similar mitigating influence on the accumulation of sea- ice. The 
potential influence of persistent northerly winds on the reduction of 
sea-ice concentration in northern Baffin Bay has been discussed by 
Muench (1971) and Dunbar (1973). 



89 




Figure 5.1 Enthalpy of the near surface (upper 75 m) 
layer in the NBB-NS region (referenced to 
- 1 . 8 # C) . 



90 



The North Water Process results from the combined influences of 



near-surface layer enthalpy and mechanical ice removal. Since the North 
Water is characterized by reduced ice coverage, the associated decrease 
in albedo results in the largest annual net radiation for any region 
within the Arctic Circle (Steffen and Ohmura , 1985). Admixture of 
glacial runoff creates a strong, shallow pycnocline which effectively 
confines insolation effects to the near-surface layer. Such inherent 
stratification would normally restrict convective overturn associated 
with surface freezing to shallower depths. Mechanical ice removal, 
however, results in a proportionally greater rate of brine formation 
which increases the vertical extent of mixing. Complete 
removal of the enthalpy in this near surface layer delays significant 
sea-ice formation accordingly. Divergent cyclonic currents and 
northerly winds then serve to reduce sea -ice accumulation for the 
remainder of winter. It is the self-perpetuating nature of the North 
Water Process which accounts for its persistence. 



91 



vi. DISCUSSION 



The comprehensive nature of this analysis mandates further 
examination of certain relevant topics. A combination of elaboration 
and postulation will be employed in this regard. 

The dilution of WGC water masses, relative to those which enter the 
NBB-NS region through the Canadian Archipelago, is a consequence of the 
more extensive shelf-driven modification effects inherent in the 
former. The assertion by Muench (1971), that the major proportion of 
Arctic Ocean Water is less dense than Baffin Bay Water, was derived from 
point data sources, under the assumption that there are significant 
differences in water structures between the upper 250 m layers of the 
Arctic Ocean and Baffin Bay. Muench further concludes that these water- 
structure differences create a proportionally higher surface elevation 
in the Arctic Ocean, resulting in net southward transport. 

An examination of the dynamic topography of the NBB-NS region 
reveals an obvious lack of north-south dynamic height gradients (refer 
to Figure 4.2). This is due to the fact that ABPW and WGCPW have a 
common origin in the Arctic Basin, and are quite similar in thermohaline 
character. What is apparent, however, is a distinct dynamic height 
gradient normal to the coastline. Although the increase in dynamic 
heights in the onshore direction can be viewed as a consequence of the 
influence of the Coriolis force on the prevailing baroclinic flow, it 
may alternately be considered as a driving force for the observed 
circulation in the NBB-NS region. 

The ubiquitous glaciers in the region provide a significant coastal 
source of meltwater, an influence which mav he still ic lent to drive a 



92 



geos trophically -balanced current with the shoreline on the right, in the 
direction of flow. The implication of this hypothesis is that a 
progressive winter weakening in near-surface currents would be expected 
throughout the NBB-NS region. Lemon and Fissel (1982) provided evidence 
of just such an occurrence in northwestern Baffin Bay. 

On a larger scale, the concentration of glacial meltwater within 
the NBB-NS region results in near-surface layer dilution relative to the 
saltier waters of the North Atlantic. It is the difference in near- 
surface water structure between these regions that may drive the net 
southward baroclinic transport. A progressive winter decrease in this 
net southward transport would be expected accordingly. 



93 



vii. gfiacms^Ma 



The physical oceanography of the northern Baffin Bay - Nates Strait 
region has been investigated using a dense network of CTD stations 
occupied by the CCGS SIR JOHN FRANKLIN in September 1986. The following 
major conclusions can be drawn: 

* Five water masses can be delineated in the region. The WGC is the* 
source of WGCPW and WGCAIW, while ABPW and NSAIW are derived from 
the Arctic Basin via the Canadian Archipelago. WGCAIW and NSAIW 
are prevented by shoaling of the sea floor from entering Smith 
Sound and Kane Basin, respectively. BBSW is found seasonally 
throughout northern Baffin Bay. 

* The waters unique to the WGC are subject to more extensive 
dilution effects by shelf-driven processes and are comparatively 
less saline than their Canadian Archipelago derived counterparts. 

* Bathymetry provides a significant influence on the flow of the 
WGC, which attains a maximum baroclinic transport of 0.7 Sv in 
Melville Bay. Recurvature of component branches of the WGC occurs 
primarily in Melville Bay (0.2 Sv) , south of the Carey Islands (0.1 
Sv), and ultimately in Smith Sound (0.2 Sv) . 

* The Baffin Current originates as an ice-edge jet in Smith Sound, 
subsequently proceeding southward along the coast of Ellesmere 
Island and throughout northwestern Baltin Bav. Transport ol the 



94 



Baffin Current is augmented by net outflow from Kane Basin, Jones 
Sound and Lancaster Sound at rates of 0.3 Sv, 0.3 Sv and 1.1 Sv, 
respectively . 

* Circulation in Smith, Jones and Lancaster Sounds can be described 
in terms of the GEC model, in which estuarine inflow, entrainment 
and outflow are geos trophically balanced processes. 

* Although a significant portion of the meltwater derived from the 
Humboldt Glacier is recirculated by the Kane Basin Gyre (0.4 Sv) , 
the influence of glacial admixture on thermohaline structure and 
near-surface circulation is apparent throughout the NBB-NS region 

* The North Water Process results from the combined influences of 
near-surface layer enthalpy and mechanical ice removal. 



95 



AEEEMDIX 



COMPUTATIONS ASSOCIATED WITH THE GEC MODEL 

The computation of geostrophic current widths in Smith, Jones and 
Lancaster Sounds is accomplished as prescribed by Leblond (1980). The 
requisite equations and calculations are presented here. 

The ’’Coastal Current Model" of Leblond (1980) assumes geostrophic 
flow confined to the upper layer of a two-layer stratified fluid, in a 
channel of width L and depth H (refer to Figure 4.11). Assuming the 
upper layer is relatively thin with respect to the lower layer, the 
speed of interfacial waves in the fluid may be approximated as: 

g(p2-p L ) t(o) (1) 

c = 

*1 

where: g = the gravitational acceleration; 

Pi = the density of the upper layer; 
p 2 = the density of the lower layer; and 

t(o) = the thickness of the upper layer at the channel wall. 

In Smith Sound: pi *= 1025.5 kg/m 3 ; p 2 = 1027.0 kg/m 3 ; and t(o) 

* 75 m. 

In Jones Sound: pi ~ 1026.2 kg/m 3 ; p 2 = 1027.0 kg/m 3 ; and t(o) 

- 75 m. 

In Lancaster Sound: pi - 1026.0 kg/m 3 ; p 2 = 1027.0 kg/m 3 ; and t(o) 

- 150 m. 

The internal Rossby radius of deformation is defined as: 

R - C/f (2) 

where: f = the Coriolis parameter. 

The internal Froude number is defined as: 



% 



F - u/C 



(3) 



where: u « the speed of the upper layer flow. 

In Smith Sound: u - 0.25 m/s. 

In Jones Sound: u * 0.16 m/s. 

In Lancaster Sound: u * 0.50 m/s. 

The Rossby number is defined as: 



(4) 



where: r = the radius of curvature of the flow. 

In Smith Sound: r - 25 km. 

In Jones Sound: r * 75 km. 

In Lancaster Sound: r = 60 km. 

The width of the geostrophic current is then defined as: 

Y o (5) 



97 



LIST OF REFERENCES 



Aagaard, K. , and L.K. Coachman, The East Greenland Current north of the 
Denmark Strait, I, Arctic . 21, 181-200, 1968. 

Bourke, R.H., R.G. Paquette, and A.M. Weigel, MIZLANT 85 data report: 

results of an oceanographic cruise to the Greenland Sea, September, 
1985, Tech. Rep. NPS 68-86-007, Dept, of Oceanography, Naval 
Postgraduate School, Monterey, California, 1986. 

Coachman, L.K. and K. Aagaard, Physical oceanography of Arctic and 

subarctic seas, in Arctic Geology and Oceanography , edited by Y. 
Herman, pp . 1-72, Springer- Verlag , New York, 1974. 

Dunbar, I.M., Winter regime of the North Water, Trans . R . Soc . Can . , 
4(9), 275-281, 1973. 

Fissel, D.B., D.D. Lemon, and J.R. Birch, Major features of the summer 
near-surface circulation of western Baffin Bay, 1978 and 1979, 
Arctic . 35, 180-200, 1982. 

Garrison, G.R., H.R. Feldman and P. Becker, Oceanographic measurements 
in Baffin Bay, Unpublished manuscript. Applied Physics Laboratory, 
University of Washington, February, 1976. 

Leblond, P.H., On the surface circulation in some channels of the 
Canadian Arctic Archipelago, Arctic , 35, 189-197, 1980. 

Lemon, D.D. and D.B. Fissel, Seasonal variations in currents and water 
properties in northwestern Baffin Bay, 1978 and 1979, Arctic , 35, 
211-218, 1982. 

Melling, H., R.A. Lake, D.R. Topham, and D.B. Fissel, Oceanic thermal 
structure in the western Canadian Arctic, Continental Shelf 
Research , 3, 233-258, 1984. 

Muench, R.D., The physical oceanography of the northern Baffin Bay 

region. Baffin Bay-North Water Pro j . Arct. Inst. North Am. Sci. 
Rep. , 1-72, 1971. 

Muench, R.D., and H.E. Sadler, Physical oceanographic observations in 
Baffin Bay and Davis Strait, Arctic , 26, 73-76, 1973. 

Sadler, H.E., Water, heat, and salt transports through Nares Strait, 
Ellesmere Island, J. Fish. Res. Board Can. . 33, 2286-2295, 1976. 

Steffen, K. and A. Ohmura , Heat exchange and surface conditions in the 
North Water, northern Baffin Bay, Ann . Glaciology . 6, 178-181. 

1985. 



98 



Tunnicliffe, M.D., An investigation of the waters of the East Greenland 
Current, Master's Thesis, Naval Postgraduate School, Monterey, 
California, September 1985. 



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Thesis 
A24257 
c. i 



Addison 

The physical oceano- 
graphy of the northern 
Baffin Bay-Nares Strait 
region.